Backing pumps more particularly for volatile liquids

ABSTRACT

A backing pump 4 for volatile fuel is constructed as an axial flow helical impeller pump operating in a cylindrical housing, having a tapered coaxial inlet portion at one end for connection to a small-diameter inlet line and a volute outlet at the other end. The helical vane extends to near the minimum diameter housing part at the inlet so that the pumped liquid, as it is accelerated through the length of the housing, will be substantially confined to an external part of progressively increasing inside diameter leaving a central &#39;&#39;&#39;&#39;fluid hub&#39;&#39;&#39;&#39; portion separated from it by a boundary zone and having little axial movement due to centrifugal action, vapors and gases will collect in the fluid hub, thus ensuring a substantially bubblefree outlet.

0 ilmte States Patent [72] Inventor Peter J. Taylor Ilford, England [21]Appl. No. 6,175

[22] Filed Jan. 27, 1970 [45] Patented Jan. 4, 1972 73] Assignee ThePlessey Company Limited Ilford, England [32] Priority Jan. 31, 1969 [33] Great Britain [54] BACKING PUMPS MORE PARTICULARLY FOR 50FieldoigiijjjiIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 415/72,1l6;417/199A, 203, 20s

[5 6] References Cited UNITED STATES PATENTS 2,782,595 2/1957 Pauly417/203 2,845,870 8/1958 Lock 415/72 Primary Examiner-C. J. HusarAttorneyScrivener, Parker, Scrivener and Clarke ABSTRACT: A backing pump4 for volatile fuel is constructed as an axial flow helical impellerpump operating in a cylindrical housing, having a tapered coaxial inletportion at one end for connection to a small-diameter inlet line and avolute outlet at the other end. The helical vane extends to near theminimum diameter housing part at the inlet so that the pumped liquid, asit is accelerated through the length of the housing, will besubstantially confined to an external pan of progressively increasinginside diameter leaving a central fluid hub portion separated from it bya boundary zone and having little axial movement due to centrifugalaction, vapors and gases will collect in the fluid hub, thus ensuring asubstantially bubble-free outlet.

- 16 I 8 GI "15 BACKING PUMPS MORE PARTICULARLY FOR VOLATILE LIQUIDS Inpumping systems for volatile liquids, and more particularly in aircraftfuel supply systems in which the liquid is to be delivered under highpressure by a volumetric pump, it is common to arrange at the inlet sideof this pump a socalled backing pump in order to maintain an adequateinlet pressure for the volumetric pump, and it is usual to provide sucha backing pump even in cases in which a transfer pump is arranged in thefuel tank or other point of liquid supply. Such backing pumps havehitherto been constructed as centrifugal pumps, which offer a highflexibility of output, but conditions may arise with volatile liquids,for example in the case of inoperativeness of a transfer pump orexhaustion of the supply of one of the transfer pumps, in which theliquid reaching the backing pump is liable to contain a high volumetricpercentage of free vapor or gas (air) which, in the case of acentrifugal pump, may lead to depriming of the centrifugal pump and aconsequent breakdown in pumping.

The present invention has for an object to provide an improved pumpsuitable for use as a backing pump for liquid which is volatile orliable to contain gases and/or vapors. Another object is to provide anaxial flow impeller pump in which the flow of liquid is substantiallyconfined to an annulus adjacent the circumferential wall of the pumpingchamber while leaving a comparatively inert central core which increasesin diameter from the inlet to the outlet as, due to the action of theimpeller blades, the velocity of liquid increases from the inlet endtowards the outlet end. This will ensure an outlet relatively free fromgas and vapor bubbles.

The diameter of the inlet portion of the pump housing is preferablyflared from a small diameter at the inlet towards a cylindrical portionand the helical impellers blades preferably commence near the smallestdiameter portion of the housing so as to act upon the liquid as soon asit enters the pump, thus avoiding the hydrodynamic losses normallyconnected with a diffusor.

A fuel system incorporating a backing pump according to the inventionconstitutes another aspect of the invention.

One embodiment of the invention will now be described in more detailwith reference to the accompanying drawing, which is a diagrammaticrepresentation of a fuel system including a backing pump which is shownin axial section.

Referring now to the drawing, the illustrated fuel system includes afuel tank 1 equipped with a transfer pump 2 which ensures the transferof fuel from the tank 1, for example a wingtip tank of an aircraft to afuel transfer line 3 which leads via a backing pump 4 to a fuel meteringand pressurizing pump 5, the latter is associated with a fuel controlsystem 6 for the supply of fuel to a point of consumption illustrated asa burner nozzle 7. Under certain conditions, which often occur inhighaltitude flight, the fuel in line 3 reaching the backing pump 4 isliable to be near its boiling point and, as a result of this, fuelentering the backing pump 4 is liable to contain a high volumetricpercentage of free vapor and of gases which had been dissolved in thefuel. The presence of such gaseous admixtures render the use of acentrifugal backing pump unreliable. The backing pump employed accordingto the present invention is an axial flow impeller pump which has agenerally cylindrical housing 8 which is formed at its inlet end with aflared portion 9 to provide .a small inlet diameter substantially equalto that of the adjoining end 10 of the fuel transfer line 3, while theoutlet end of the housing 8 is formed as a volute 11 whose outlet ductportion 12 is connected to the inlet of a metering pump 5 by a line 13.Accommodated in the housing is an impeller rotor mounted on a shaft 14.This rotor has a substantially cylindrical hub portion 15. From a pointnear the inlet end of the flared housing portion 9 and throughout thecylindrical housing portion 8, and which is equipped with four helicalvanes 16 which extend from the hub into close proximity of the wall ofthe pumping chamber to form a fourstart impeller. The rotor is arrangedto be rotated in the direction of the arrow A so that its helical turnswill axially impel liquid towards the volute 11. During operation of thepump, any liquid entering the housing chamber through the inlet 10 willbe progressively accelerated both in the axial and tangential directionsas it passes through the length of the housing portions 9 and 8.

Since the volume of the liquid remains constant during its passagethrough the pump, it follows from the increase in its axial velocitythat the cross section, taken at right angles to the rotor axis, of themoving flow of liquid between the circumferential wall of the housingportions 9, 8 and the rotor hub 15 will decrease on its way from theentrance portion 10 to the volute ll of the pump housing, and since, dueto the tangential acceleration, the liquid will also assume a swirlingmotion about the rotor axis, this flow will, due, to centrifugal action,be confined to the outermost parts of the cross section, of the housingchamber. The liquid in the remaining part of the pump housing, i.e. thepart nearer the rotor axis although forming a continuous body of liquidwith the liquid participating in this flow, will be substantially inertinasmuch as it has no effective axial velocity but merely participatesin the rotation of the rotor, thus constituting a kind of liquid hub,and it will be appreciated that, due to the centrifugal action, anyparticles of free gas or vapor in the flow of liquid which moves fromthe inlet to the volute, will be displaced from the outer zone in whichthe liquid flows, causing the particles to move towards the axis of therotor into this liquid hub through the large area of direct liquidcontact of the latter with the flow of axially moving liquid. Therefore,if the pump is arranged for vertical upward flow, as is preferred, theseparticles can rise within this liquid hub towards the volute of thepump, which they will reach between the axis of the volute and the zonewhich is entered by the flow of pumped liquid; from this part of thevolute they are preferably conducted, as pointed out further below,through apertures 18. It will be observed that the helical vanes 16 ofthe rotor, which extend into close proximity of the cylindrical portion8 of the housing, extend well into the flared housing portion 9, wherethey increase in diameter in accordance with the cone angle, from apoint close to the minimum diameter entry portion 10 of the housing,thus ensuring that impeller action is already effective in the flaredportion 9 of the housing. This will ensure that the liquid being pumpedis accelerated throughout its way through the pump housing and avoidspressure losses which are liable to occur in increasing diameterportions of fluid conduits where diffuser action is relied upon toconvert kinetic energy into pressure.

The helical impeller action can be utilized to obtain an appreciableincrease in fluid pressure from the inlet to the outlet of the pump, andthis will be conducive for the vapor and gas liberated from the incomingliquid at the entry of the pump, where the liquid is at its lowestpressure, to become recondensed or redissolved as the pressure of thepumped liquid increases towards the outlet end of the pump. In view ofthe centrifugal forces acting, this recondensation will take place inthe vicinity of the border zone 17 between the zone of pumped liquid andthe fluid hub, so that any implosive action connected withrecondensation will take place well away from the housing wall and theimpeller hub, thereby largely avoiding any socalled cavitation damage.Any unabsorbed residue of gaseous components which may reach the volute11, can be readily withdrawn by a vent system 18 connected to the voluteat a convenient point of the liquid hub zone between the axis of thepumping chamber and the border zone 17.

Various details of the construction described with reference to thedrawing may be modified without exceeding the scope of the invention.Thus the number of helical vanes need not necessarily be four but may bevaried according to other considerations.

What we claim is:

1. An axial flow impeller pump, comprising a housing provided with ahousing chamber having a longitudinal axis and a wall surface in theform of a surface of revolution about this axis, and with an axiallydirected inlet at one end of the chamber and open at its other end to avolute which is approximately coaxial with said chamber; an impellerrotor mounted in this housing for rotation about said axis, said rotorhaving helical blades operative to apply, during rotation of the rotor,axial acceleration as well as tangential acceleration to any liquidentering the housing chamber through said inlet, with the crosssectionalarea of the bladed rotor permitting the ratio of the total cross sectionavailable in the housing chamber for axial flow, to the cross sectionrequired for the axial flow of the amount of liquid actually passingthrough the pumping chamber, to increase progressively from the inletend of the housing towards the volute, so that centrifugal action willcause the formation, inside a peripheral zone of liquid flowing from theinlet to the volute, of an inner body of liquid having substantially noeffective axial velocity, said inner body of liquid being continuouswith the liquid in said zone and extending into the volute chamberbetween said zone and the axis of the pumping chamber from a point nearthe inlet.

2. A pump as claimed in claim 1 wherein the blades of the impeller arein the form of a pluralstart helix.

3. A pump as claimed in claim 1, wherein the housing chamber has acylindrical main portion and an inlet portion which is coaxial with thesaid main portion and is flared to increase from a small diameter at theinlet end of the housing chamber to reach, at its junction with the mainportion of the housing chamber, the diameter of the said main portion.

4. A pump as claimed in claim 3, wherein the helical blades extendaxially substantially throughout the length of the housing chamber froma point closely adjacent to the inlet.

5. A pump as claimed in claim 1, wherein the pump housing is providedwith bleed aperture communicating with the volute at a point radiallyinside the surface of revolution separating the flow of pumped liquidfrom the inner body of liquid having no effective axial velocity.

6. A fuel system, which comprises an axial flow pump as claimed in claim1, a fuel tank, a transfer pump associated with said fuel tank fortransferring fuel from said pump axial flow pump, and a pressurizingpump having an inlet connected to the volute of said axial flow pump.

1. An axial flow impeller pump, comprising a housing provided with ahousing chamber having a longitudinal axis and a wall surface in theform of a surface of revolution about this axis, and with an axiallydirected inlet at one end of the chamber and open at its other end to avolute which is approximately coaxial with said chamber; an impellerrotor mounted in this housing for rotation about said axis, said rotorhaving helical blades operative to apply, during rotation of the rotor,axial acceleration as well as tangential acceleration to any liquidentering the housing chamber through said inlet, with the crosssectionalarea of the bladed rotor permitting the ratio of the total cross sectionavailable in the housing chamber for axial flow, to the cross sectionrequired for the axial flow of the amount of liquid actually passingthrough the pumping chamber, to increase progressively from the inletend of the housing towards the volute, so that centrifugal action willcause the formation, inside a peripheral zone of liquid flowing from theinlet to the volute, of an inner body of liquid having substantially noeffective axial velocity, said inner body of liquid being continuouswith the liquid in said zone and extending into the volute chamberbetween said zone and the axis of the pumping chamber from a point nearthe inlet.
 2. A pump as claimed in claim 1 wherein the blades of theimpeller are in the form of a plural-start helix.
 3. A pump as claimedin claim 1, wherein the housing chamber has a cylindrical main portionand an inlet portion which is coaxial with the said main portion and isflared to increase from a small diameter at the inlet end of the housingchamber to reach, at its junction with the main portion of the housingchamber, the diameter of the said main portion.
 4. A pump as claimed inclaim 3, wherein the helical blades extend axially substantiallythroughout the length of the housing chamber from a point closelyadjacent to the inlet.
 5. A pump as claimed in claim 1, wherein the pumphousing is provided with bleed aperture communicating with the volute ata point radially inside the surface of revolution separating the flow ofpumped liquid from the inner body of liquid having no effective axialvelocity.
 6. A fuel system, which comprises an axial flow pump asclaImed in claim 1, a fuel tank, a transfer pump associated with saidfuel tank for transferring fuel from said pump to said axial flow pump,and a pressurizing pump having an inlet connected to the volute of saidaxial flow pump.